I'll offer 3 comments (but I think no surprises) ...

You haven't told us what they were screaming, nor we know how the Yahoo 
Group or LISTSERV list was setup, nor do we know how you prepared them 
for the change, except to say a change was coming.  It's hard to comment 
w/o something more concrete.

Except in very special, brief circumstances, I've always had a policy 
that discussing the list or problems one has with the list is off-topic 
and not welcome on-the-list!   Whenever there is something new, people 
get frustrated, and with some, the frustration turns to anger beyond 
reason.  Some people skip right past frustration and express their anger 
immediately (Case in point: the idiot on TV with Mike Meyers from LA 
this past weekend).    I had one list where I setup another list for 
discussion of the first.  It was used for a couple of years (until the 
membership matured).

Yahoo Groups offers a beautiful interface, albeit with advertisements.  
LISTSERV offers a very good interface with tremendous capability and 
flexibility, but not quite as slick when used for the first time.  Also, 
a list owner has more freedom to tailor the LISTSERV interface to the 
audience.

Hope this helps!

cheers, wayne

C. William Westerfield wrote, in part,  on 9/5/2005 6:32 PM:

>I recently had the painful experience of converting a Yahoo Groups! Forum
>(of over 600 subscribers) to LISTSERV.  The pain wasn't in the technical
>conversion.  That was, of course, a breeze.  The pain came in the torrents
>of emails that followed with people screaming about the "disastrous" move.
>  
>